I’m building a new engine for the 92x Saab ’05. Having gone from a ’00 Explorer v8, I am missing my torque. Moving up to a 2.5 could be the best opportunity for improvement.

Started the project with a core short block, please see pics below with splitting the case halves and cleaning all the surfaces and oil relieving the major passages. The oil relieving pictures are a little hard to see, so I pointed to where the action is taking place.
next, I picked up a set of STI rods, this was more cost effective then the eagle H beams. (I’m not planning for 400ph) The rods were balanced end to end to the extent I could accurately repeatedly measure them.
Then, I balanced the pistons. A quiet engine was more important than additional strength. I choose stock STIs over Wisecos. I'm going to have to be careful to run conservative manifold pressures. This will be addressed later, as the car is tuned.
Time for assembly! I cleaned all my parts twice then went into the clean room to start assembling the short block. I lubed the crankshaft, and laid out my rods and friction coated rod bearings. I lubed my bearings, and then installed the rods onto the crank.
The main bearings aren't here yet so I’m jumping to the cylinder heads, and then come back to the short block. Since the Saab is my daily driver, and still running fine, we will start from a set of core heads. Cleaned and disassembled, they are now ready for port work!
In the pics below you can see the weight savings of the newer style bucket vs the old. First design is heavier and adds considerable weight to the valve motion. I will be converting these heads over to the newer design to save valve train weight.
Another way to save valve train weight is by using lightweight titanium retainers. They will work with the stock springs.
The coated main bearings showed up so I’m jumping back to the short block assembly! Heres my fancy coated main bearings, ready to be installed.
The other side of the engine gets the same treatment, then the case halves are bolted together and torqued to spec.
Here are pic of moving back to the cylinder heads, and starting the port work. The goal for the heads was to get some additional flow to compliment the larger 2.5 motor. I started in the mill by D shaping the inside of the port. This will give me some solid boundaries to help keep the size/shape very consistent from port to port. The idea was to get a little more flow but not going too radical since the camshaft selection is pretty mild. Don’t want to lose any response by making the volume too large. Once the mill had done its job I hand blended everything to my satisfaction and worked the seat transition and angles.
I will confesss, I got a little carried away with the heads, but they turned out great! In these pictures you can see I hand blended the upper most valve angle back into the chambers.
Rather than reuse the valves that came out of the spare heads, I grabbed a set of hollow stem STI valves off the shelf and cleaned them up so they could be faced. The intake valves are back cut with 2 additional angles for a total of 3 angles. The exhaust valves will have only one additional back cut angle, for a total of 2.

Next I started lapping the valves and double checking the contact surface on the valve as well as the valve seat. You can see I dyed the valve seat to make it more obvious how uniform the actual 45deg seat is cut. No need to dye the valve its pretty easy to read.

I dyed the TGV outlet and cylinder head inlet and scribed them against a reusable 2 piece LGT intake gasket. This will allow a perfect union between the parts and also give me a point of reference as I modify airflow in the pinch point of the TGV (by the fuel injector). The TGV was totally disassembled, the divider was removed via the mill, then I hand ported it. You can see the radius around the injector where I increased the cross-sectional area at the pinch point.
I scribed rings around the chamber to mark the location of the bore of a 2 liter, and the bore of a 2.5 liter. Then measured the chamber diameter of an STI head and established it is midway between the 2. The goal was to enlarge the chamber a bit to try to keep the compression as low as possible, but not make the chamber walls too thin. The logical approach would be to try and machine the 2 liter chamber to the same size of the 2.5, however the chambers of the STI are significantly larger, and felt this would make the walls of the 2 liter chamber thin, negatively affecting the rigidity of the deck surface and ultimately compromising the sealing capacity of the head gasket. So, deciding to split the difference, grind to the first mark, enlarge the chamber a bit, and live with some added compression, I’m more than comfortable with a small increase in static compression. Next it was polished out like the rest of the chamber, and I started getting ready for a chemistry experiment.

I took a step back today and decided to unshroud the valves.
This caused me to have to polish out the chamber sides again but
it wasn’t too much additional work. This will help flow, and also
give me slightly more chamber volume as well.
You can see the various stages of chamber finish.
Today I CC’d the finished chambers to measure for uniformity,
as well as compare against a stock STI head so that the
static compression ratio could be calculated.
The measured size of my chambers was 52cc and the
measured size of the STI chamber was 57cc. The STI
compression ratio should be 8.2:1 using a stock piston.
My compression ratio should be 8.7:1 and I feel that’s
easily within the desired range of what I have planned for this engine.
Tonight I jumped back to the bottom end to wrap up the short block
and get it mounted on a stand. Indexed the rings, after
measuring them, there was only about ½ thou difference in
ring gap so no need to gap them. Next the pistons,
wristpins and locks were installed. Then, the plugs, covers,
and rear main seal were installed.
The holes thru the center of the TGV’s, were tapped and plugged.
I installed stock valves and measured them for height,
so there would be a point of reference. Once I had
the measurements, I started the process of shortening
the STI valves to the same installed height.
As a side note I quickly weighed the stock wrx and hollow sti
valves to see what kinda weight difference there is.
As you can see its minimal but every little bit helps!
Next I installed new valve seals,and began to assemble the heads.
Valves go in first being sure to lube the ends where they have to slide thru new valve
seals. We have some 09 WRX valve springs, some titanium retainers,
and stock Subaru spring seats and locks.
Cylinder head assembly is pretty straight forward but we took some pictures anyway!

The camshafts are another heavy item that can be improved upon.
The first picture shows the weight of a standard wrx cam.
The second photo shows the weight of the newer style hollow core 2.5L cams.
The STI cams also have a little more lift and duration too, so it makes for a great swap.
These are meant for varriable valve timing, so theres a little bit of modification that
has to happen to block off the additional oil passages in the cams.

Who is online

Users browsing this forum: No registered users and 1 guest

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum